This project considers certain features of aging cells in culture. The first portion deals with "Mixed Function Oxidation and Modification of Collagen" and "Prolyl Hydroxylase in Aging Fibroblast Cultures". The second portion examines the role of a vitamin K dependent bone protein recently discovered in our laboratory in the etiology of senile osteoporosis. This protein, termed osteocalcin is involved in the calcium metabolism and structure of mineralized tissues. The third project examines the status of the "Low Density Lipoprotein Receptors in Aging Cells" and examines the cell age dependence in the regulation of cholesterol biosynthesis. Preliminary evidence suggests that the number of LDL receptors decreases with the "age" of diploid fibroblast culture. The fourth project examines various X-linked parameters and indices of cell aging. In particular, it currently examines the X-linked HGPRT (hypoxanthine-guanine phosphoribosyl transferase system) and compares it to the autosome linked APRT (adenine phosphoribosyl transferase) system as a function of cell age. In general, this program examines a variety of cell and tissue "age" dependent properties and could be of considerable importance in geriatric medicines. BIBLIOGRAPHIC REFERENCES: Keith, D.A., Paz, M.A. and Gallop, P.M. The effect of Diphenylhydantoin on fibroblasts in vitro. J. Dent. Res. Nov. 1977. in press.